In recent years, many intensive studies have been made on IP (Internet Protocol) for mobile communication networks.
The IETF (Internet Engineering Task Force) is proceeding with efforts to standardize Mobile IPv6 specifications. The essential elements comprising a Mobile IPv6 network are a mobile node (hereafter expressed as MN), a home agent (hereafter expressed as HA), a correspondent node (hereafter expressed as CN), and an access router (hereafter expressed as AR).
The basic operation of Mobile IPv6 is described next. An IP address (home address, hereafter expressed as HoA) that does not change even if the MN has moved, is assigned to the MN1. Therefore, an application that starts up on the MN can continue running without stopping even if the MN is moving. A network possessing a network prefix identical to the HoA is called a home network. When the MN moves to a network (host network) other than the home network, it acquires an IP address that conforms to the communication protocol within that host network. This IP address is called the Care of Address (hereafter expressed as CoA).
The MN receives a router advertisement (RA) sent periodically from the AR located in the host network. If the network prefix detected at this time that is different from the HoA, then this signifies movement has been detected and a CoA is then generated. The MN that detected movement sends to the HA, a position registration message (Binding Update: BU) requesting the relay of a packet for an MN destination sent to the home network. The HA that received the binding update creates a binding cache to link the MN home address with the care of address (CoA). The HA afterwards sends a position registration reply message (Binding Ack: BA) to the MN, and broadcasts a packet acquisition message (Gratuitous Neighbor Advertisement: G-NA) as a proxy for receiving the packet addressed to the MN moving in the host network. The CN is the communication correspondent node (other communication party) for the MN. The CN sends a packet addressed to the HoA of the MN. The HA receives as a proxy, the HoA addressed packet for the MN. The HA searches the Binding Cache and acquires a CoA corresponding to the HoA for the MN. The HA attaches (encapsulates) an IP header for the CoA that matches the original received packet and sends that packet. The MN removes (decapsulates) the encapsulated header of the CoA. The CN can then receive the packet sent addressed to the HoA of the MN, which is the original packet.
However, in the technology of the related art the MN cannot identify movement of the mobile terminal until a router advertisement is received from the AR installed within the host network at the movement destination. The packet from the CN cannot be received during this time, because a new CoA cannot be generated and position registration messages (binding updates) cannot be exchanged due to failure to identify movement of the mobile terminal.    [Non-patent document 1] D. Johnson et. al. “Mobility Support in IPv6”, IETF 2003,    http://www.ietf.org/internet-drafts/draft-ietf-MobileIP-IPv 6-24.txt